Stator Endwinding Vibration in Two-Pole Machines: Copyright Material IEEE, Paper No. PCIC-2018-51

In the past 15 years, insurance industry data indicates stator endwinding vibration has become the most important cause of failure in generators. The source of vibration is the current creating magnetic forces between coils and may be amplified due to mechanical resonance. Endwinding vibration leads to failure by insulation abrasion or copper fatigue cracking. The extent of the repair due to the ensuing damage and the loss of production have proven to be very costly. After 13 years of operation one such failure occurred to a 2-pole, 95MW generator at a plant in Indonesia with an associated loss of $40 million. This paper describes the failure mechanism, the possible reasons why endwinding vibration has become a more important issue in the past decade, and a new IEC standard 60034–32 on methods to detect the problem well before in-service failure. A case study on the affected generator will show how a repeat stator winding failure was avoided using these tools.